1. Field of the Invention
The present invention relates to pharmacogenetics and cardiology. More specifically, the present invention relates to methods for individualized heart failure therapy with bucindolol based on a patient's genotype of polymorphisms in adrenergic receptor genes, including the β1-adrenergic receptor (β1AR) gene and the α2c-adrenergic receptor (α2cAR) gene.
2. Description of Related Art
According to the American Heart Association (AHA), about 62 million Americans have some form of cardiovascular disease, which can include high blood pressure, coronary heart disease (heart attack and chest pain), stroke, birth defects of the heart and blood vessels, and congestive heart failure, and close to a million die from such conditions every year. The annual report of the AHA further states that cardiovascular disease kills more Americans than the next seven causes of death combined, including cancer. Surprisingly, slightly more females, overall, than males have cardiovascular disease. Heart disease accounted for 40% of all deaths in the U.S. in 1999. Despite recent treatment advances, mortality from heart failure is approximately 50% within 5 years.
In the United States alone there are approximately six million people, about 1.5% of the population, with chronic heart failure (“HF”), and 550,000 new patients are diagnosed each year. Medical therapy has made progress in treating HF, but morbidity and mortality remain high (Mann et al., 2005). The current standard of care in HF involves the use of inhibitors (ACE inhibitors, ARBs, and/or aldosterone receptor antagonists) of the renin-angiotensin-aldosterone system (RAAS), and β-blockers, which competitively inhibit β-adrenergic receptors on cardiac myocytes. β-blockers are effective in mortality reduction and are considered the most effective HF drug class overall, but still work in only 50-60% of treated patients. Moreover, the U.S. patient clinical data on the efficacy of approved β-blockers in mortality trials is less impressive, with published data from the only large, intention-to-treat mortality trial showing an increase in mortality in U.S. patients vs. placebo.
Accordingly, there is a substantial need for improved HF therapies that have higher efficacy and response rates, are better tolerated, and are better suited to subpopulations with special needs, such as diabetics. However, development of new agents against this therapeutic background has proved extremely challenging. Since 2001, of 13 Phase III trials in HF only three have been positive. Two of these positive trials were with an ARB (candesartan) (McMurray et al., 2003; Granger et al., 2003). The third positive trial, the A-HeFT Trial with BiDil (a combination of isosorbide dinitrate and hydralazine) was in a subset (African-Americans) that comprises only 12% of the American HF population (Taylor et al., 2004). Clearly, there is a continued need to develop the next generation of HF drugs.
While β1 agonists are used for treating acute deterioration of patients with failing ventricular function, prolonged exposure of the heart from administered agonists, or the elevated catecholamine agonists produced by the body, leads to worsening heart failure. In contrast, β-adrenergic receptor antagonists (termed β-blockers) have emerged as a major treatment modality in chronic heart failure.
In the early 1990's, a group of U.S. heart failure investigators working with β-blocking agents in heart failure decided that a mortality trial was required in order to validate this still-controversial therapy. A group of U.S. drafted a protocol and grant application that was subsequently approved for funding by the VA cooperative Clinical Studies Program and the NHLBI. The approved protocol did not specify a drug, but rather provided that an optimal β-blocker would be selected based on potential for success and strength of Phase II data. The drugs that were considered were carvedilol, metoprolol tartrate, metoprolol succinate CR/XL, and bucindolol. Metoprolol tartrate was rejected because of less than promising effects on mortality from the MDC Trial (Waagstein et al., 1993); metoprolol succinate CR/XL was not selected because of a lack of efficacy and tolerability data in heart failure; and carvedilol was not selected in part because of poor tolerability in advanced heart failure (Krum et al. 1995). Bucindolol was the unanimous choice of the Selection Committee, based on its excellent tolerability (Eichhorn et al., 1997; Gilbert et al., 1990; Bristow et al., 1994; Pollock et al., 1990), efficacy (Gilbert et al., 1990; Bristow et al., 1994; Pollock et al., 1990; Eichhorn et al., 1990), and level of interest by its sponsor. Bucindolol thus became the subject of the Beta Blocker Evaluation of Survival Trial (“BEST”), the first mortality trial planned and initiated in HF.
The BEST trial began in 1995, and ended in 1999. After BEST was initiated three other mortality trials were planned and initiated, MERIT-HF with metoprolol succinate CR/XL (MERIT-HF Study Group, 1999), CIBIS-II with bisoprolol (CIBIS-II Investigators, 1999), and COPERNICUS with carvedilol (Packer et al., 2002). Due to the more rapid and less restrictive enrollment of these trials, CIBIS-II and MERIT-HF were completed before BEST, and both these trials had positive results.
The BEST Trial was terminated prematurely in 1999, prior to completion, due in part to a loss of equipoise by investigators, and an accelerated drop-in rate to open label β-blockers based on the knowledge of the other two positive trials (BEST Trial Investigators, 2001; Domanski et al., 2003). The sponsor elected not to proceed with the commercial development of bucindolol based on the results known at the time the Trial was stopped. While BEST investigators observed a benefit in Class III, non-African-Americans, that was similar to the positive results reported six months earlier in CIBIS II and MERIT-HF, the investigators observed poor results in Class IV and African-American patients. Moreover, BEST did not meet its primary endpoint of all-cause mortality (reduction of 10%, p=0.10) when the trial was stopped (BEST Trial Investigators, 2001). The investigators postulated that the differences between the results of other β-blockers and bucindolol might be attributable to the “unique pharmacological properties of bucindolol” (BEST Trial Investigators, 2001), which highlights the perceived distinctions among the chemical and functional properties of this diverse class of compounds.
Moreover, even though most β-blocker trials in heart failure have shown group beneficial effects, there is substantial interindividual variability in outcome that is not explained by baseline clinical characteristics (CIBIS-II Investigators, 1999). Interindividual variability in the response to pharmacologic therapy is recognized with virtually all drugs. In circumstances such as the treatment of chronic heart failure with β-blockers—where morbidity and mortality are high, the titration algorithm is complex, the interindividual variability is substantial, and additional treatment options exist—assessing the likelihood of a favorable (or adverse) long-term response to drug therapy can have a significant impact on decision making. The approximately 50% 5-year mortality of patients with heart failure has prompted intense study of treatment options and has lead to multidrug regimens typically including a β-blocker, an angiotensin converting enzyme inhibitor (or angiotensin receptor antagonist), diuretics, and digoxin. β-blocker therapy is initiated in relatively stable patients, at low doses (i.e., about 10 mg), and slowly increased over a period of months to either a target dose, or a dose which is tolerated. Dosage adjustments of other drugs, or initiation of additional drugs is not uncommon during the up-titration period. Thus the treatment of heart failure with β-blockers must be individualized. Indeed the statement “dosage must be individualized and closely monitored” is found in the prescribing information for the two β-blocker preparations approved for treating heart failure in the U.S. Furthermore, studies in animal models and humans suggest that β-blocker-promoted reversal of the cellular and global remodeling of the failing heart may require months of stable therapy (Lowes et al., 2002). Substantial variability in responses to β-blockers has been noted, including left ventricular ejection fraction (LVEF) changes (van Campen et al., 1998), exercise tolerance (Bolger, 2003) and survival (Packe et al., 2001). Nevertheless, based on the preponderance of data, β-blocker therapy should be considered for most patients with chronic heart failure, assuming no contraindications such as volume overload, requirement for inotropic infusions, bradycardia, hemodynamic instability, and asthma.
Consequently, not only were there perceived differences among the various β-blockers—particularly bucindolol as compared to other β-blockers—but also variability had been observed among patients in their abilities to respond favorable to a particular β-blocker therapy. Evidence for the therapeutic value of bucindolol is needed, particularly evidence that explains these interindividual differences.